Definition: The Maximum value of the forward current that a PN junction or diode can carry without damaging the device is called its Maximum Forward Current. The rating of a PN junction or a diode is specified by the manufacturer in its data sheet. However, if the forward current in a diode is increased beyond this specified value, the junction will be destroyed.
When the maximum forward current increases then the depletion region of the diode will reduce. The depletion region is the region around the junction which supply the charge carriers. The small depletion region obstructs the voltage to pass through it. If the maximum current rating is raised beyond the limit, then it will damage the structure of the diode.